行動未運行

Question

主窗口：

<Window x:Class="Generator.MainWindow" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:ignore="http://www.galasoft.ch/ignore" 
    mc:Ignorable="d ignore" 
    Height="309.851" 
    Width="673.433" 
    Title="Generator" 
    DataContext="{Binding Main, Source={StaticResource Locator}}"> 

    <Grid x:Name="LayoutRoot"> 
     <Frame x:Name="MainFrame" Content="" NavigationUIVisibility="Hidden" HorizontalAlignment="Left" Height="235" Margin="0,36,0,0" VerticalAlignment="Top" Width="294" Source="/Generator;component/Pages/TCPage.xaml"/> 
    </Grid> 
</Window> 

這是內框架的頁面

<Page x:Class="Generator.Pages.TCPage" 
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation" 
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml" 
    xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006" 
    xmlns:d="http://schemas.microsoft.com/expression/blend/2008" 
    xmlns:local="clr-namespace:Generator.Pages" 
    mc:Ignorable="d" 
    d:DesignHeight="300" d:DesignWidth="300" 
    DataContext="{Binding TCPageVM, Source={StaticResource Locator}}" 
    Title="TCPage"> 

    <Grid> 
     <Button x:Name="button" Content="Jobby" HorizontalAlignment="Left" Margin="160,185,0,0" VerticalAlignment="Top" Width="75" 
      Command="{Binding ButtonCommandNew}" /> 
    </Grid> 
</Page> 

這是在頁面的模型視圖的按鈕命令（TCPageVM）：

private bool _inProgress = false; 
    private RelayCommand _buttonCommandNew; 
    public RelayCommand ButtonCommandNew 
    { 
     get 
     { 
      var worker = new TCService(); 

      return _buttonCommandNew 
        ?? (_buttonCommandNew = new RelayCommand(async() => 
        { 
         var progress = new Progress<string>(status => 
         { 
          ProgressText = status; 
         }); 

         _inProgress = true; 
         _buttonCommandNew.RaiseCanExecuteChanged(); 

         await worker.GenerateConfiguration(1, "", "", progress); 

         _inProgress = false; 
         _buttonCommandNew.RaiseCanExecuteChanged(); 

        },() => !_inProgress 

       )); 
     } 
    } 

這是服務執行：

public Task<bool> GenerateConfiguration(int cellCount, string templateFilePath, string outputFilePath, IProgress<string> progress) 
{ 
    return Task.Run(() => RunConfigurator(progress)); 
} 

private bool RunConfigurator(IProgress<string> progress) 
{ 
    Thread.Sleep(6000); 
    progress.Report("Yeah!"); 
    return true; 
} 

問題是該按鈕已啓用，但操作未運行。

Answer 1

RelayCommand不會對您傳遞給它的操作保持強烈的引用。它只保留一個弱的參考。在創建RelayCommand之後，該命令是唯一一個對您提供的操作有引用的命令。由於它是一個弱引用，因此可用於垃圾收集。啓用狀態正確反映的原因是，當開始評估時，它可能未被垃圾收集。

您可以通過將該操作作爲該類上的命名方法來解決該問題，然後將該方法傳遞給RelayCommand。您也可以將這兩個參數存儲在其他地方。底線是你需要在RelayCommand以外的地方保留一個強有力的參考。

public RelayCommand ButtonCommandNew 
{ 
    get 
    { 
     return _buttonCommandNew 
       ?? (_buttonCommandNew = new RelayCommand(ExecuteAction, CanExecuteAction)); 
    } 
} 

private async void ExecuteAction() 
{ 
    var worker = new TCService(); 
    var progress = new Progress<string>(status => 
    { 
     ProgressText = status; 
    }); 

    _inProgress = true; 
    _buttonCommandNew.RaiseCanExecuteChanged(); 

    await worker.GenerateConfiguration(1, "", "", progress); 

    _inProgress = false; 
    _buttonCommandNew.RaiseCanExecuteChanged(); 
} 

private bool CanExecuteAction() 
{ 
    return !_inProgress; 
}